I’ve had a warm place in my heart for Slim for a long time, and especially so since recognizing the Action-Domain-Responder pattern. In this post, I’ll show how to refactor the Slim tutorial application to ADR.

One nice thing about Slim (and most other HTTP user interface frameworks) is that they are already “action” oriented. That is, their routers do not presume a controller class with many action methods. Instead, they presume an action closure or a single-action invokable class. So the Action part of Action-Domain-Responder already exists for Slim. All that is needed is to pull extraneous bits out of the Actions, to more clearly separate their behaviors from Domain and the Responder behaviors.

He then works through each piece of the example application, first extracting out the Domain logic then building a Responder to handle the user interface functionality. He combines them to replace the current functionality, pointing out that the responder can now be tested separately from the user interface (templating system).

Now, for a simple case like this, using ADR (or even webbishy MVC) might seem like overkill. But simple cases become complex quickly, and this simple case shows how the ADR separation-of-concerns can be applied as a Slim-based application increases in complexity.

In a way, sending an email as part of a web request/response cycle is like sending two responses: the normal HTTP response, and the email response. With that in mind, it might make sense to think of the HTML + Text email templates as part of a presentation layer. Or, as a combination of infrastructure (the email-sending client) plus presentation (the templates). That would be how to think about the separation of concerns there.

He then provides what he sees as a good directory structure to help keep it all separated out. He also talks about the load sending emails can put on a system, when to move it to workers and how that impacts where the templating of the emails should be done.

In this post to his sitePaul Jones looks at the combination of the Action-Domain-Responder pattern and the Command Bus pattern in application development. In the post he answer the question about how they fit together.

Over the past few weeks, different people have asked me where a Command Bus goes in an Action-Domain-Responder system. While I’m not a DDD expert, after brushing up on the subject a little, my answer is: "In the Domain."

He starts by reviewing the three pieces of the ADR pattern with brief descriptions of each. The then covers the Command Bus pattern, linking to several other resources with more details about the pattern itself and a quick summary of their main points. He talks about how the overall structure is a part of the Command Query Responsibility Segregation pattern and suggests that, since the Command Bus pattern is a "fire and forget" kind of thing it belongs in the Domain of ADR. He gives a brief code example and answers other questions about validation and error handling as a part of this suggested flow.

Paul applies some of the concepts that Revath outlined to the ADR pattern, suggesting that service classes should always return Payloads and the reduction of functionality in the controller overall. He includes an example of what the resulting code would look like, following along with the "orders" scenario outlined in Revath's post.

In response to a recent post from Anthony Ferrara about MVC Paul Jones suggests that Anthony's view that it and related structures "all pretend to be application architectures" is false.

The central mistake I think Anthony makes is near the end of this post, where he states (in talking about MVC, ADR, et al.) that “All Pretend To Be Application Architectures.” That assertion strikes me as incorrect. While it may be that developers using MVC may mistakenly think of MVC as an application architecture, the pattern description itself makes no such claim. Indeed, Fowler categorizes MVC as a “Web Presentation Pattern” and not as an “Application Architecture” per se. [...] Fowler’s categorization and description of MVC define it pretty clearly as a user interface pattern. ADR, as a refinement of MVC, is likewise a user interface pattern.

He goes on to talk more about the ADR (Action-Domain-Responder) pattern, how it's more of a user interface pattern as well and how that relates to using it for HTTP requests. He suggests that the definition from Anthony may be a bit too broad and proposes the alternative "All Are User Interface Patterns, Not Entire Application Architectures" to be a bit more specific.

Paul Jones has a new post with more information about his proposed "Action-Domain-Responder" design pattern (a replacement for the typical MVC) and suggests a new piece, the Domain Payload pattern. This pattern would use a domain payload object to wrap the data and provide the responder with additional handling and context.

In Action-Domain-Responder the Action passes input to the Domain layer, which then returns some data for the Action to pass to the Responder. In simple scenarios, it might be enough for the Responder to inspect the data to determine how it should present that data. In more complex scenarios, though, it would make more sense for the Domain to pass back the data in a way that indicates the status of the data. Instead of the Responder inspecting the Domain results, the Domain should tell us what kind of results they are.

He shows a code example of this Domain Payload object in action, starting with some typical MVC code and refactoring it along the way into an ADR structure. He shifts from a typical model into a more domain-driven approach and describes the wrapping of the data in the payload, context for the contents (even just a class name helps) and how those relate to the actual output. You can find the resulting code in this example over on Paul's GitHub account.

Paul M. Jones has started an interesting discussion rethinking the MVC pattern as applied to the web, which he has dubbed Action-Domain-Responder (ADR). If you haven't given it a read yet, click the link and do that; this page will still be sitting here waiting when you return. I agree with a ton of it - heck, I've contributed to it a fair bit via conversations with Paul. But there's been one thing nagging at me for a bit now, and I was finally able to put it into words recently. Controllers - Actions in ADR - can be explained as facades.

Matthew starts off by defining the Facade design pattern with a quote from the infamous "Gang of Four" book: simply put, a simplified interface to a complex system. He provides a basic example of a facade that wraps some common steps for inserting and logging data with this kind of simplified interface. He applies this to the ADR pattern's controllers, pointing out that it handles a few complex steps "behind the scenes" common to marshaling and managing the request.

For me, thinking of Controllers and Actions as Facades has an additional benefit: it describes rather complex architectural patterns in terms of basic design patterns. I find the more I can reduce the complexity of a definition, the more likely I will understand and use it correctly.

In his latest post Paul Jones has proposed a "tentative MVC refinement" as the structure behind your application. He suggests something called the action-domain-response pattern, focusing on some of the more common practices in web application development today instead of an ideal.

The term MVC has experienced some semantic diffusion from its original meaning, especially in a web context. Because of this diffusion, the Action-Domain-Response pattern description is intended as a web-specific refinement of the MVC pattern. I think ADR more closely fits what we actually do in web development on a daily basis. [...] We generally route and dispatch not to a controller class per se, but to a particular action method within a controller class. It is also partly revealed by the fact that we commonly think of the template as the View, when in a web context it may be more accurate to say that the HTTP response is the View. As such, I think ADR may represent a better separation of concerns than MVC does in a web context.

He goes through the structure he's worked up, showing the interaction between the parts and compares the flow to a typical MVC-based application. He also mentions a few other MVC pattern alternatives including Data-Context-Interaction and Model-View-ViewModel. He then gets into an actual code-based example using a typical blog application. He compares the directory structure and proposes that instead of one controller per file it becomes one action per file (and one response per file accordingly).